Abundance and distribution of South Australia's endemic sea star, Parvulastra parvivipara (Asteroidea: Asterinidae)

Abstract

Parvulastra parvivipara is one of the smallest sea stars. It is restricted to tide pools on seven granite platforms within 200 km of coastline on the Eyre Peninsula of South Australia. This species exhibits intragonadal brooding and cannibalism of offspring, and gives birth to non-dispersive juveniles. Its distribution is variable, with specimens occupying few of the many seemingly similar tide pools at each site at differing densities. The abundance and distribution of P. parvivipara were examined in relation to twelve ecological variables of tide pools at all known mainland sites. An estimate of overall population size was also made. Multiple regression analyses showed that the abundance of P. parvivipara was negatively associated with wave-exposure and positively associated with the structural complexity of tide pools. A multiple logistic regression also indicated that the presence of sea stars (distribution) was more likely in structurally complex tide pools with low wave-exposure. Additionally, increasing elevation of a tide pool relative to the high-tide margin within the intertidal zone reduced the likelihood of finding sea stars. It is suggested that the variable abundance and distribution of P. parvivipara may be driven by broad scale ecological variables (e.g. complexity and wave-exposure), localised population extinctions (within tide pools) and recolonisation of tide pools via transportation of individuals across the rock platforms by wave-energy. It is also suggested that strikingly high abundances of P. parvivipara in some tide pools are likely to result from the reproductive mode of this species where each hermaphroditic individual gives birth to cohorts of up to twenty non-dispersive juveniles.